1. Field of the Invention
The present invention relates to a fresh water generator and a fresh water generating method for desalinating a target liquid containing residual chlorine by feeding the same to a fresh water generating cartridge having a reverse osmosis membrane.
2. Description of the Prior Art
When desalinating a target liquid (hereinafter referred to as raw water) such as service water or industrial water containing residual chlorine, a fresh water generator having a fresh water generating cartridge including a reverse osmosis membrane (RO membrane) separates the raw water into permeated water and concentrated water. In order to obtain permeated water in a necessary and sufficient flow rate in a fresh water generator having a limited scale, a permeated water storage tank is provided on the fresh water generator for storing unused permeated water therein or a pressure pump is provided on the fresh water generator for increasing the permeate flow rate per unit membrane area.
FIG. 8 is a block diagram showing an exemplary conventional fresh water generator having a pressure pump 100.
The fresh water generator shown in FIG. 8 employs the pressure pump 100 and a fresh water generating cartridge 4 for desalination. The fresh water generating cartridge 4 includes a reverse osmosis membrane. The reverse osmosis membrane is reduced in durability when exposed to chlorine for a long time, and hence an active carbon cartridge 2 is employed for pretreatment in order to remove residual chlorine contained in raw water.
The raw water is fed to the active carbon cartridge 2 through a raw water feed pipe 1. The pressure pump 100 feeds the water permeating the active carbon cartridge 2 as pretreated water to the fresh water generating cartridge 4 through a pretreated water feed pipe 3. The fresh water generating cartridge 4 having the reverse osmosis membrane separates the pretreated water into permeated water and concentrated water. The separated permeated water is taken out from the fresh water generating cartridge 4 as treated water through a permeated water outlet pipe 5. On the other hand, the concentrated water is discharged from the fresh water generating cartridge 4 through a concentrated water discharge pipe 7. The concentrated water discharge pipe 7 is provided with a pressure regulating valve 6, for suppressing the concentrate flow rate. Thus, permeation through the membrane is prompted in the fresh water generating cartridge 4.
However, the aforementioned fresh water generator requires a driver (not shown) such as a motor or an engine for driving the pressure pump 100 and a controller (not shown) for controlling the driver. Thus, the fresh water generating cost as well as the price of the fresh water generator increase. Further, noise generated in the pressure pump 100 and the driver results in a problem.
When fresh water generation work with the fresh water generator is stopped over a long period, bacteria propagate in the fresh water generating cartridge and are mixed into permeated water when fresh water generation work is restarted, to deteriorate the quality of the permeated water.
An object of the present invention is to provide a fresh water generator which can be reliably operated at a low cost while preventing a permeated liquid from deterioration of quality resulting from propagation of bacteria with no problem of noise.
Another object of the present invention is to provide a fresh water generating method which can be reliably carried out at a low cost while preventing a permeated liquid from deterioration of quality resulting from propagation of bacteria with no problem of noise.
The inventor has made various experiments and deep study for desalinating a target liquid without employing a pressure pump while suppressing propagation of bacteria, to find out that it is possible to desalinate a target liquid having a pressure of not more than 2 kgf/cm2 by feeding the same to a fresh water generating cartridge having a reverse osmosis membrane without employing a pressure pump when employing a reverse osmosis membrane having a performance of a rejection of at least 95% for an NaCl aqueous solution of 0.05% in concentration and a permeate flow rate of at least 0.1 m3/m2xc2x7dayxc2x7kgf/cm2.
The inventor has also found out that propagation of bacteria in the fresh water generating cartridge can be suppressed by feeding the target liquid to the fresh water generating cartridge through a pretreater for removing residual chlorine while properly feeding the target liquid to the fresh water generating cartridge while bypassing the pretreater. The inventor has proposed the present invention on the basis of such recognition.
A fresh water generator according to an aspect of the present invention comprises a fresh water generating cartridge, including a reverse osmosis membrane, for desalinating a target liquid, a pretreater provided in the preceding stage to the fresh water generating cartridge for removing residual chlorine contained in the target liquid, a feed system feeding the target liquid having a prescribed pressure to the pretreater without through a step-up device stepping up the pressure of the target liquid, a bypass path provided to bypass the pretreater and an opening/closing device opening and closing the bypass path.
In this fresh water generator, the target liquid having a prescribed pressure is fed to the pretreater so that residual chlorine contained therein is removed. The target liquid obtained from the pretreater is fed to the fresh water generating cartridge having the reverse osmosis membrane, and desalinated. If the target liquid from which the residual chlorine having a bactericidal function is removed remains in the fresh water generating cartridge, bacteria readily propagate therein. Therefore, the opening/closing device opens the bypass path, so that the target liquid containing residual chlorine can be fed to the fresh water generating cartridge. Thus, propagation of bacteria can be suppressed in the fresh water generating cartridge. Consequently, the permeated liquid is prevented from deterioration of quality resulting from propagation of bacteria.
In the fresh water generator, the target liquid having a prescribed pressure is fed to the fresh water generating cartridge through the pretreater in a non-powered manner without through a pressure pump serving as a step-up device, whereby neither a driver for driving the pressure pump nor a controller for controlling the driver is necessary. Thus, the fresh water generating cost is reduced while increase of the price of the fresh water generator is suppressed. Further, no problem of noise is caused by any pressure pump or driver. In addition, the fresh water generator requiring no pressure pump, no driver and no controller is miniaturized and no electric charge is required.
If the time interval for feeding the target liquid containing residual chlorine to the fresh water generating cartridge through the bypass path is longer than 12 hours, the bactericidal effect of residual chlorine contained in the target liquid fed to the fresh water generating cartridge through the bypass path is lost and propagation of bacteria is disadvantageously prompted. If the time interval for feeding the target liquid containing residual chlorine to the fresh water generating cartridge through the bypass path is shorter than 10 minutes, on the other hand, the flow rate of a wastefully discharged target liquid is uneconomically increased. Therefore, the time interval for feeding the target liquid containing residual chlorine to the fresh water generating cartridge through the bypass path is preferably at least 10 minutes and not more than 12 hours.
If the time for feeding the target liquid containing residual chlorine to the fresh water generating cartridge through the bypass path is shorter than 5 seconds, propagation of bacteria in the fresh water generating cartridge cannot be sufficiently suppressed. If the time for feeding the target liquid containing residual chlorine to the fresh water generating cartridge through the bypass path is longer than 5 minutes, on the other hand, the reverse osmosis membrane may be damaged. Therefore, the time for feeding the target liquid containing residual chlorine to the fresh water generating cartridge through the bypass path is preferably at least 5 seconds and not more than 5 minutes, and more preferably at least 15 seconds and not more than 2 minutes.
The prescribed pressure may be at least 0.3 kgf/cm2 and not more than 3 kgf/cm2. In this case, desalination can be performed without employing a pressure pump.
The opening/closing device may periodically open the bypass path. In this case, the target liquid containing residual chlorine having a bactericidal function is periodically fed to the fresh water generating cartridge, thereby periodically suppressing propagation of bacteria in the fresh water generating cartridge.
The opening/closing device may temporarily open the bypass path and thereafter close the bypass path when fresh water generation work with the fresh water generating cartridge is started. In this case, the target liquid containing residual chlorine having a bactericidal function is fed to the fresh water generating cartridge when starting fresh water generation work, so that bacteria having propagated in the fresh water generating cartridge during stoppage of fresh water generation work can be disinfected and sterilized. Thus, propagation of bacteria in the fresh water generating cartridge is suppressed during fresh water generation work, and the permeated liquid is prevented from deterioration of quality resulting from propagation of bacteria.
The opening/closing device may open the bypass path during fresh water generation work with the fresh water generating cartridge. In this case, the target liquid containing residual chlorine having a bactericidal function is fed to the fresh water generating cartridge during fresh water generation work, so that bacteria propagating in the fresh water generating cartridge during fresh water generation work can be disinfected and sterilized. Thus, propagation of bacteria in the fresh water generating cartridge is suppressed during fresh water generation work, and the permeated liquid is prevented from deterioration of quality resulting from propagation of bacteria. In this case, the bypass path may be periodically or non-periodically opened during fresh water generation work.
The opening/closing device may open the bypass path simultaneously with stoppage of fresh water generation work with the fresh water generating cartridge. In this case, the target liquid containing residual chlorine having a bactericidal function is fed to the fresh water generating cartridge simultaneously with stoppage of fresh water generation work, so that bacteria propagating in the fresh water generating cartridge during fresh water generation work can be disinfected and sterilized. Thus, propagation of bacteria in the fresh water generating cartridge is suppressed during stoppage of fresh water generation work, and the permeated liquid is prevented from deterioration of quality resulting from propagation of bacteria.
The opening/closing device may open the bypass path during stoppage of fresh water generation work with the fresh water generating cartridge. In this case, the target liquid containing residual chlorine having a bactericidal function is fed to the fresh water generating cartridge during stoppage of fresh water generation work, for suppressing propagation of bacteria in the fresh water generating cartridge during stoppage of fresh water generation work. Thus, the permeated liquid is prevented from deterioration of quality resulting from mixture with propagating bacteria when fresh water generation work is restarted.
The ratio b/a of the flow rate b of the permeated liquid obtained from the fresh water generating cartridge to the flow rate a of the target liquid fed to the fresh water generating cartridge may be so set that b/a greater than 0.5.
In desalination with the fresh water generating cartridge having the reverse osmosis membrane, the target liquid fed to the fresh water generating cartridge is separated into a permeated liquid from which impurities are removed and a concentrated liquid in which impurities are concentrated. In order to increase the linear velocity on the surface of the reverse osmosis membrane for maintaining the membrane performance, the permeate flow rate b may be minimized so that the concentrate flow rate (a-b) approaches the target liquid flow rate a. When the ratio b/a of the permeate flow rate b to the target liquid flow rate a is minimized to 0.1 or 0.2, for example, the linear velocity on the surface of the reverse osmosis membrane is maintained in a state close to that on the inlet for the target liquid. However, the concentrated liquid is generally discarded and hence the flow rate b of the essentially required permeated liquid is uneconomically reduced if the ratio b/a of the permeate flow rate b to the target liquid flow rate a is at a low value.
In the fresh water generator according to the present invention, propagation of bacteria can be suppressed in the fresh water generating cartridge by providing the bypass path on the pretreater, whereby the quality of the permeated liquid can be maintained even if the ratio b/a of the permeate flow rate b to the target liquid flow rate a exceeds 0.5. Consequently, an economical permeate flow rate can be obtained.
The fresh water generating cartridge may be formed by a plurality of fresh water generating cartridges connected in parallel and/or in series with each other. In this case, a large volume of permeated liquid can be obtained while preventing deterioration of the quality of the permeated liquid resulting from propagation of bacteria.
The opening/closing device may include an opening/closing valve. In this case, the target liquid containing residual chlorine can be fed to the fresh water generating cartridge through the bypass path by opening the opening/closing valve while the target liquid containing residual chlorine can be fed to the pretreater by closing the opening/closing valve.
The opening/closing value may include a first automatic valve, and the fresh water generator may further comprise a first controller controlling an opening and closing operation of the first automatic valve. In this case, the first controller automatically controls the opening and closing operation of the first automatic valve.
The first controller may control the first automatic valve to open the first automatic valve by a prescribed time at a prescribed time interval. Thus, the target liquid containing residual chlorine is periodically and automatically fed to the fresh water generating cartridge through the bypass path. Consequently, propagation of bacteria can be automatically suppressed in the fresh water generating cartridge.
The fresh water generator may further comprise a flushing device for flushing the reverse osmosis membrane of the fresh water generating cartridge. The term xe2x80x9cflushingxe2x80x9d indicates an operation of washing the surface of a separation membrane with a water stream.
In this case, impurities remaining on the surface of the reverse osmosis membrane of the fresh water generating cartridge can be discharged from the fresh water generating cartridge by flushing the reverse osmosis membrane of the fresh water generating cartridge with the flushing device. Consequently, it is possible to prevent deterioration of the quality of the permeated liquid in a short period and reduction of the permeate flow rate over time caused by an insufficient linear velocity on the surface of the reverse osmosis membrane.
The flushing device may periodically perform the flushing operation. Thus, impurities remaining on the surface of the reverse osmosis membrane of the fresh water generating cartridge can be periodically discharged from the fresh water generating cartridge.
The flushing device may perform the flushing operation when fresh water generation work with the fresh water generating cartridge is started. Thus, impurities such as fungi generated and deposited in the fresh water generating cartridge during stoppage of fresh water generation work can be discharged from the fresh water generating cartridge.
The flushing device may perform the flushing operation during fresh water generation work with the fresh water generating cartridge. Thus, impurities remaining on the surface of the reverse osmosis membrane of the fresh water generating cartridge during fresh water generation work can be discharged from the fresh water generating cartridge. In this case, flushing may be periodically or non-periodically performed during fresh water generation work.
The flushing device may perform the flushing operation simultaneously with stoppage of fresh water generation work with the fresh water generating cartridge. Thus, impurities remaining on the surface of the reverse osmosis membrane of the fresh water generating cartridge during fresh water generation work can be discharged from the fresh water generating cartridge.
The flushing device may perform the flushing operation during stoppage of fresh water generation work with the fresh water generating cartridge. Thus, impurities such as fungi generated and deposited in the fresh water generating cartridge during stoppage of fresh water generation work can be discharged from the fresh water generating cartridge.
The flushing device may be a flushing valve stored in the fresh water generating cartridge. Alternatively, the flushing device may be a flushing valve provided in a concentrated liquid path of the fresh water generating cartridge. In this case, the concentrate flow rate is increased by opening the flushing valve to increase the linear velocity on the surface of the reverse osmosis membrane of the fresh water generating cartridge. Thus, impurities remaining on the surface of the reverse osmosis membrane are discharged from the fresh water generating cartridge.
If a plurality of fresh water generating cartridges are provided in parallel or in series with each other, the flushing valve may be stored in each fresh water generating cartridge or may be provided on the concentrated liquid path of each fresh water generating cartridge. Alternatively, the flushing valve may be provided on the rearmost one of connected portions between the concentrated liquid paths of the plurality of fresh water generating cartridges. Further, a prescribed number of fresh water generating cartridges arranged in parallel or in series with each other with a flushing valve provided on the rearmost one of connected portions between the concentrated liquid paths thereof may be integrated into a unit so that a plurality of such units are arranged in parallel or in series with each other.
The flushing valve may include a second automatic valve, and the fresh water generator may further comprise a second controller controlling an opening and closing operation of the second automatic valve. In this case, the second controller automatically controls the opening and closing operation of the second automatic valve.
The second controller may control the second automatic valve to open the second automatic valve by a prescribed time at a prescribed time interval. Thus, the second automatic valve is periodically and automatically opened for periodically flushing the fresh water generating cartridge. Consequently, impurities remaining on the surface of the reverse osmosis membrane are periodically discharged from the fresh water generating cartridge.
The opening/closing device may include a first automatic valve, the flushing device may include a second automatic valve, and the fresh water generator may further comprise a controller independently or simultaneously controlling opening and closing operations of the first automatic valve and the second automatic valve respectively. In this case, the controller automatically controls the opening and closing operations of the first automatic valve and the second automatic valve independently of or simultaneously with each other.
Preferably, the opening/closing device opens the bypass path at a first time interval c, the flushing device performs the flushing operation at a second time interval d, and the ratio c/d of the first time interval c to the second time interval d is so set that c/dxe2x89xa71.
If the ratio c/d of the first time interval c to the second time interval d is less than 1, the frequency of feeding the target liquid containing residual chlorine to the fresh water generating cartridge by opening the first automatic valve is increased to deteriorate the quality of the permeated liquid. Further, the first automatic valve attains a sufficient effect of suppressing propagation of bacteria through single opening with respect to one or more flushing operations of the second automatic valve. Therefore, it is possible to prevent deterioration of the quality of the permeated liquid by setting the ratio c/d of the first time interval c to the second time interval d to at least 1.
The fresh water generator may be provided with a permeated liquid outlet path taking out a permeated liquid obtained from the fresh water generating cartridge and a permeated liquid discharge path discharging the permeated liquid. In this case, the permeated liquid taken out from the permeated liquid outlet path is employed for various applications as desalinated water. On the other hand, the permeated liquid discharged from the permeated liquid discharge path is not used but discharged as waste water.
In the fresh water generator thus provided with the permeated liquid discharge path, impurities deposited in the fresh water generating cartridge can be discharged from the fresh water generating cartridge through the permeated liquid discharge path along with the permeated liquid. The permeated liquid containing a large amount of impurities is discharged through the permeated liquid discharge path and hence only a permeated liquid having high quality is taken out from the permeated liquid outlet path. Therefore, the permeated liquid taken out from the permeated liquid outlet path is prevented from contamination with impurities and deterioration of quality.
In the aforementioned fresh water generator, further, raw water containing residual chlorine fed to the fresh water generating cartridge through the bypass path can be treated with the fresh water generating cartridge and thereafter discharged through the permeated liquid discharge path. Thus, the fresh water generating cartridge and the outlet for the permeated liquid are sterilized and propagation of bacteria can be suppressed.
The permeated liquid may be periodically discharged through the permeated liquid discharge path. Thus, impurities deposited in the fresh water generating cartridge can be periodically discharged from the fresh water generating cartridge through the permeated liquid discharge path along with the permeated liquid.
The permeated liquid may be discharged through the permeated liquid discharge path when fresh water generation work with the fresh water generating cartridge is started. Alternatively, the permeated liquid may be discharged through the permeated liquid discharge path during stoppage of fresh water generation work with the fresh water generating cartridge. In this case, impurities deposited in the fresh water generating cartridge during stoppage of fresh water generation work can be discharged from the fresh water generating cartridge through the permeated liquid discharge path.
The reverse osmosis membrane may have a performance of a rejection of at least 95% for an NaCl aqueous solution of 0.05% in concentration and a permeate flow rate of at least 0.1 m3/m2xc2x7dayxc2x7kgf/cm2. In this case, the target liquid having a prescribed pressure can be fed to the fresh water generating cartridge without employing a pressurizer for readily performing desalination.
A fresh water generating method according to another aspect of the present invention comprises steps of feeding a target liquid having a prescribed pressure to a fresh water generating cartridge including a reverse osmosis membrane through a pretreater removing residual chlorine without through a step-up device stepping up the pressure, and feeding the target liquid to the fresh water generating cartridge while bypassing the pretreater at prescribed timing.
In this fresh water generating method, the target liquid having a prescribed pressure is fed to the pretreater so that residual chlorine contained in the target liquid is removed. The treated liquid obtained from the pretreater is fed to the fresh water generating cartridge having the reverse osmosis membrane and desalinated. When the treated liquid from which residual chlorine having a bactericidal function is removed remains in the fresh water generating cartridge, bacteria readily propagate therein. When feeding the target liquid to the fresh water generating cartridge while bypassing the pretreater at prescribed timing, therefore, the target liquid containing residual chlorine can be fed to the fresh water generating cartridge. Thus, propagation of bacteria can be suppressed in the fresh water generating cartridge. Consequently, the permeated liquid is prevented from deterioration of quality resulting from propagation of bacteria.
In this fresh water generating method, further, the target liquid having a prescribed pressure is fed to the fresh water generating cartridge in a non-powered manner without employing a pressure pump as a step-up device through the pretreater, whereby neither a driver for driving the pressure pump nor a controller for controlling the driver is required. Therefore, the fresh water generating cost is reduced and increase of the price of a fresh water generator is suppressed. Further, no problem of noise is caused by any pressure pump or driver.
The fresh water generating method may further comprise a step of flushing the reverse osmosis membrane of the fresh water generating cartridge at prescribed timing. Thus, impurities remaining on the surface of the reverse osmosis membrane of the fresh water generating cartridge can be discharged from the fresh water generating cartridge. Consequently, it is possible to prevent deterioration of the quality of the permeated liquid in a short period and reduction of the permeate flow rate over time caused by an insufficient linear velocity on the surface of the reverse osmosis membrane.
The fresh water generating method may further comprise a step of discharging a permeated liquid obtained from the fresh water generating cartridge through a permeated liquid discharge path at prescribed timing. In this case, impurities deposited in the fresh water generating cartridge and on the outlet for the permeated liquid can be discharged from the fresh water generating cartridge along with the permeated liquid. The permeated liquid containing a large amount of impurities is discharged through the permeated liquid discharge path, and hence no discharged impurities are mixed into the permeated liquid taken out from the permeated liquid outlet path. Therefore, the permeated liquid is prevented from deterioration of quality and a permeated liquid having high quality can be obtained. Further, water containing residual chlorine fed to the fresh water generating cartridge through the bypass path can be treated with the fresh water generating cartridge and thereafter discharged through the permeated liquid discharge path, whereby propagation of bacteria can be suppressed in the fresh water generating cartridge and on the outlet for the permeated liquid.
The fresh water generating method may further comprise a step of applying the permeated liquid obtained from the fresh water generating cartridge to wash water, soft water for a boiler, soft water for preparing food, agricultural water for hydroponics, pure water for a laboratory, water for a humidifier or potable water.
The fresh water generating method may further comprise a step of feeding the permeated liquid obtained from the fresh water generating cartridge to an ion exchanger or a continuous electric regenerative ion exchanger. In this case, purity of the permeated liquid is further improved by the ion exchanger or the continuous electric regenerative ion exchanger, whereby extrapure water is obtained.